Today's supply chain is highly complex, diverse, and extensive. While globalization has optimized resource allocation and reduced manufacturing cost, it also exposes the supply chain to more risks, such as counterfeiting and theft. As a result, track-and-trace technologies have become increasingly important for protecting commercial and personal assets against various adversaries experienced during supply chain distribution. Though current track-and-trace technologies provide manufacturers, distributors, and retailers with systematic methods to detect and control these adversaries, they oftentimes can be cost-ineffective, inefficient, and/or insecure.
Traditionally, both barcodes and quick response (QR) codes have been used to track and trace commodities in the supply chain [3,4]. Though these codes (e.g., QR codes) can be encrypted to inhibit unauthorized access [5,6], they are easily duplicable due to the visibility and controllability of the pixel information revealed therein. In addition, other shortcomings such as, for example, requirement of individual scanning, direct line of sight between the reader and the code, and close proximity to reader all severely impact the overall utility of traditional track-and-trace technologies.
Radio frequency identification (RFID) is growing in popularity as a replacement of barcodes and QR codes in various industries such as commercial retail and governmental agencies [8]. Compared to barcodes and QR codes, an RFID-based scheme supports batch-scanning, does not require a direct line of sight for access, and needs less human involvement to collect data, making automated track-and-trace possible. A series of encryption techniques such as, for example, advanced encryption standard (AES), public-key cryptography, and elliptic curve cryptography (ECC), have been proposed to enhance the security and privacy of RFID tags [9-11]. Despite these enhanced security measures, however, the relatively higher price of an RFID tag limits its applications in the supply chains of low-cost commodities.
Recently, cost-effective RFID tags that do not contain a microchip (i.e., chipless) in the transponder have gained interest due to extremely low price (as low as 0.1 cents) that enables their applications in the supply chain of low-cost commodities, and elimination of tag memory that protects commodities from the threat of denial-of-service attack performed in the form of overwriting tag memory.
Currently available chipless RFID tags, however, require either the removal or shorting of some resonators (e.g., spirals slots or patch slots) from the tag substrate in order to encode data [17-19]. When one resonator is removed or shorted, the resonance point associated with that resonator will be either removed from the spectrum or shifted outside of the frequency band of interest. One bit is encoded to ‘1’ when the corresponding resonance point exists at a specific frequency, and ‘0’ when the resonance point disappears, or vice versa. Removal of resonators will incur a waste of tag area. Shorting resonators ensures that the same layout with all the resonators shorted can be used to produce different chipless RFID tags. When encoding data, the shorting can be removed using laser cutting or conventional etching techniques. Removing and shorting resonators will increase the manufacturing time and/or cost of chipless RFID tags. Furthermore, the IDs generated by these chipless RFID tags are deterministic and predictable, and thus are easily clonable. Small ID size not exceeding 35 bits and large tag area also limit the utility of conventional chipless RFID tags.
For certain commodities such as, for example, pharmaceuticals, food, and beverages, it is necessary or desirable to monitor environmental factors such as storage temperature during distribution in order to keep the efficacy, quality, and/or flavor of the commodities in check. However, currently there is no cost-effective solution for tracking the temperatures of commodities utilizing existing track-and-trace technologies.